Electrical plug



Aug. 30, 1938. G. H. BURT ELECTRICAL PLUG Filed March 23, 1938 Z L y A TTORNEYS.

Patented Aug. 30, 1938 NITED This invention relates to an electrical connector or plug, and more particularly to an improved electrical cord connector plug of the type commonly employed to attach a circuit cable or extension cord to a heater such as an electric iron, toaster orother electrical appliance.

An object of the invention is to provide an improved electrical connector construction having means whereby the electrical contacts and W the connector wires attached thereto within the plug are relieved from extreme pulling strains such as when the plug is withdrawn from the socket of the appliance by seizure of the cable.

Another object of the invention is to provide w an improved cord connector plug construction having means for firmly gripping and anchoring the extension cord or cable thereto whereby the plug may be easily separated from the socket by a straight axial pull on the cable without inflicting detrimental strain on either the connector wires or the contacts within the plug structure.

Another object of the invention is the provision of an electrical cord connector of the above character having anchoring means for the extension cord as it emerges from the plug designed so as to relieve the contact and connector wires within the structure from torsional strain when the extension cord is subjectedto a torque by being twisted.

A further object of the invention is to provide an electrical plug and cord assembly in which the grip on the cord will be sumcient to prevent within certain tolerances a pull or torque applied to the cord outside of the plug from being so transmitted to the part of the cord within the plug as to cause a movement of the cord parts within the plug beyond certain limits.

With these and other objects in view, the invention consists of certain novel features of construction, as will be more fully described, and

particularly pointed out in the appended claims.

In the accompanying drawing: Fig. 1 is a vertical elevational view of. an electrical cord connector plug formed of a pair of sections in opposed face to face relation embodying my invention;

Fig. 2 is an elevational view of the connector (oi. ire-e22) Fig. 5 is an enlarged sectional view of a frag,- mental portion of the showing of Fig; 4 with the wire and the recess therefor greatly enlarged;

Fig. 6 is a. longitudinal sectional view taken on the line tb of Fig. 1;

Fig. 7 is a plan view of the connector plug shown in Fig. 1 but with the extension cord removed;

Fig. 8 is a perspective view of a fragmental portion of the plug;

Figs. 9 and 10 are fragmental sectional views showing various modifications of recesses in the portion of the plug which grips the connector cord.

Fig. 11 is a view similar to Fig. 3 of a modified 15 form of section of connector plug;

It is well-known practice in the use of ordinary electrical cord attachment plugs that such devices are many times withdrawn from the socket of the electrical appliance by seizure and 20 sudden jerking oi the cable or extension cord, thereby causing extreme strain to be imposed on the connection wires of the cable with the contacts of the plug and consequently resulting in'a rapid destruction and deterioration of the 3 portion of the cable adjacent to the plug. Further, twisting of the cord often occurs causing a difi'erent strain to be transmitted to and into the plug. The strain placed on these extension cords under these conditions often is of such force that many times the connector wires of the cable where they are attached to the metal contacts of the plug are broken and short circuits result; and in order to obviate such difilculties I have provided an electrical cord con- 35 nector plug construction having means disposed within the plug so constructed and arranged as to prevent the connection between the wires and the contacts within the plug from being materially strained by reason of excessive 40 tension or torque being transmitted thereto if the cable is pulled or twisted; and in order to accomplish these advantageous results I have provided in each of the sections of the connector plug adjacent the rear opening thereof through 45 which the extension cord extends into the connector block, anchoring means adapted to bite into exterior portions of the cable or extension cord that is clampedvbetween the sections for firmly gripping and holding the cord preferably at oppositely disposed points upon sections of the plug in opposed face to face relation whereby any force applied to the cable will be borne by such anchoring and gripping means of the plug and will so relieve the cord within the plug that these forces will not be imposed to a substantial degree or a degree to cause deterimental movement upon the connector wires within the plug; and the following is a more detailed description of the present embodiment of this invention, illustrating the preferred means by which these advantageous results may be accomplished:

With reference to the drawing, l0 designates generally the electrical cord connector or attachment plug and comprises a body member generally oblong in cross-section formed of opposedhalves or sections H and E2 of hard rubber or other suitable hard insulating material. The sections H and i2 are of substantially identical construction and they are held in face to face contact with each other by means of suitable screws M and nuts l5, as is the usual construction of such connector plugs. The opposed faces of the sections H and I2 are formed with spaced complementary longitudinal grooves or recesses of generally rectangular cross-section Ill and i8 which cooperate to form parallel contact housing channels or sockets extending inwardly from the forward end of the connector plug when the body pieces ii and i2 are clamped together. The shape of these channels is not material so long as they fit the contacts of the plug.

In each of these sockets in the front of the insulating plug comprising sections H and I2 there is mounted a pair of opposed resilient metal contacts 20 and 2! which are of the usual construction employed for connector plugs of this type, and are of substantially semi-tubular formation from sheet stock. The contacts 20 and 2! each present split terminal sockets for the reception,

of the contact prongs or blades carried by the electrical appliance. As shown in Fig. 2, the inner ends of each pair of the contacts and 2| are flattened, as indicated at 22, and they are fixed to the plug consistingpf sections i I and I2 in any suitable and well-known manner. The grooves l1 and H! in the sections II and I2 are of a size sufficient to leave a slight clearance between the contact strips 20 and 2| respectively, in order to permit the same to expand laterally when in tight gripping engagement with the inserted terminal pins, blades or prongs of the usual appliance.

As shown in Fig. 2, the back end of the plug body is hollow and provided with a laterally disposed chamber 25 of generally V-shape formation for accommodating the connector wires of the extension cord C, the forward portion of the chamber 25 communicating with the rear end portions of the recesses l1 and 18 to permit attachment of the connector wires to the wiring terminal ends of said contacts 20 and 2| Formed in the rear wall of the sections are a series of axially disposed semi-cylindrical recesses 26 and 21 which are of stepped formation and which provide in the assembly of the sections of the plug cylindrical openings. These openings communicate with the chamber 25 in the plug by means of an axially disposed opening 28 which is formed by opposed recesses in the inner end wall of the chamber 25. The opening 21 is made of larger diameter than the opening 26 and is adapted to receive and hold the usual flanged sleeve, not shown, through which the extension cord C extends into the interior of the connector plug, and in which the usual cord encircling spring, not shown, is anchored, as the common construction of such cord connector plugs.

In order to tightly grip and anchor the cord secured to the plug connector against considerable torsional movement or excessive outward pulling and to prevent the transmission of strain to the connector wires and contacts within the plug, the inner surface of the opening 28 on the flange which projects inwardly from the sides is of such size as to tightly grip the cord, and in order to assist this gripping, I have provided on the face of the opening 28 of the inner end wall of the chamber 25 projections extending inwardly at oppositely disposed points toward the axis of the plug and having portions adapted to bite into the exterior surface of the cord, but of such structure as not to cut the threads thereof upon clamping of the cord between the sections it and i2, respectively.

As shown in my preferred construction illustrated in Figs. 3 and 7 of the drawing, a plurality of laterally extending projections or pins 39 are provided on the recessed face of the end wall de- -fining the part of the rear opening 28 of each section H and i2, and these projections are in the form of tapered blunt-ended pins of equal length to allow for accommodation of the twowire cord, which terminate close to the axis of the rear opening of the plug when the clamping blocks are assembled and clamped together in opposed relation, in which instance, the pins act tobite into but do not cut the outer envelope of the extension cord from opposite sides, whereby the cord is-tightly clamped and held anchored in position.

As shown in Fig. 5, the middle pin 30a serves as a positioning or separating pin, whereas the pins 301) on either side thereof serve to press into I each of the individual two wires and deform the same sufiiciently so as to provide a firm and secure grip thereon. The asbestos covering beneath the braid of the cord c fills in the spaces between the pins 30 which maintains a firm binding relation on the cord.

In view of the above description, it will be apparent that when it is desired to withdraw 'the plug from the appliance socket by pulling with the fingers on the extension cord or cable, that any pressure or straight axial pull of up to and over fifty pounds and/or twisting movement or torque of over three pounds will be carried direct ly by the projections 30 and will not be applied to any material amount to the connector wires where they are attached to the contacts within the body of the plug.

Other variations of the gripping surface of course will be readily apparent and I have shown in Figs. 9 and 10 a recess on one section of the plug and a projection on the other section to bind between the recess and the projection the cord and hold it firmly locked in the connector plug. In Figure 9 the recess 52 is shown as plain with a series of spurs or projections 53 on the other section to extend into this recess to lock the material in position. In Fig. 10 the recess 54 is provided with notches 55 to accommodate the projection 56 and its detents 51 for locking the cord in position.

In Fig. 11 the same structure as provided in the recess at 28 with its projections 30 is duplicated in a smaller size by reason of a projection 60 with pins 6| extending therefrom for gripping the individual wires 62 such as shown in Fig. 2 and locking them individually in position.

The foregoing description is directed solely towards the construction illustrated, but I desire it to be understood that I reserve the privilege of resorting to all the mechanical changes to which the device is susceptible, the invention being de- 75 fined and limited only by the terms of the appended claims.

I claim:

1. An electrical cord connector plug comprising a body of insulating material formed in two meming an entrance for the connector wires of an extension cord when the same are attached to the wiring terminals of said contact members, and a plurality of generally parallel prongs on said members, each prong being molded integral with one of said members and extending from the wall of said rear end opening toward the wall of the rear end opening of the other member, normal to the abutting surface of said member and free from undercut or overhanging portions with respect to any surface remote from the abutting surface to permit a molding die to be withdrawn therefrom, the walls of said opening and prongs being so constructed and arranged as to grip and flatten out the cord engaged, one of the prongs being so located as to engage substantially the mid portion of the cord and another of said prongs being substantially spaced therefrom and at a location suflicient to engage a side portion of the cord and prevent substantial twisting of the cord in the opening or slipping of a cord relative to the body members. i

2. An electrical cord connector plug comprising a body of insulating material formed in two members each having an abutting face to contact the other, said members providing complementary recesses at one end forming contact housing channelswhen the body pieces are together, a plural-. ity of metal contact members in said channels, said body members being provided at the other end with an opening at the rear end of the plug body communicating with said channels providing an entrance for the connector wires of an extension cord when the same are attached to the wiring terminals of said contact members, and a plurality of generally parallel prongs on said members, each prong being molded integral with one of said members and extending from the wall of said rear end opening toward the wall of the rear end opening of the other member, normal to the abutting surface of said member and free from undercut or overhanging portions with respect to any surface remote from the abuttingsurface to permit a molding die to be withdrawn therefrom, the walls of said opening and prongs being so constructed and arranged as to grip and flatten out the cord engaged, said prongs being substantially spaced and so located as to engage on either side of the mid portion of the cord and prevent substantial twisting of the cord in the opening or slipping of the cord relative to the body members.

GUY H. BURT. 

